Imaging apparatuses described above include one that has a zoom lens barrel having a zoom function which changes an imaging magnification by moving plural lens units (including a lens and its holding member) in an optical axis direction (see Japanese Patent Laid-Open No. 2001-324663).
In the zoom lens barrel disclosed in Japanese Patent Laid-Open No. 2001-324663, a plurality of lens units are moved in the optical axis direction by cams formed on a cam tube which can rotate around the optical axis. Here, a plurality of lens units are prevented from rotating so as not to rotate around the optical axis together with the cam tube. In other words, a plurality of lens units are driven in the optical axis direction by rotations of the cam tube while being guided in the optical axis direction.
Imaging apparatuses are desired to have a higher magnification ratio, but on the other hand they are required to be smaller and in particular thinner so that they can be easily carried around. A multistage stretching structure that shortens the size in the optical axis direction of each tubing member in the zoom lens barrel is conceivable for both the high magnification ratio and the low profile. However, the multistage stretching structure makes it difficult to arrange the cams for driving a plurality of lens units without interfering with each other.
Japanese Patent No. 3,842,087 discloses a zoom lens barrel provided with a first and a second cam for moving first and second lens units in the optical axis direction respectively on an outer circumferential surface and an inner circumferential surface of a rotation tube so that the first and second cams are provided without interfering (intersecting) with each other.
In the lens barrel disclosed in Japanese Patent No. 3,842,087, an outer circumferential tube arranged on an outer circumferential side of the first lens unit that is arranged closest to an object and an inner circumferential tube arranged on an inner circumferential side of the cam tube are guided (or moved linearly) in the optical axis direction by a common fixed tube. In this way, the fixed tube needs a long linearly moving guide groove, and the outer circumferential tube and the inner circumferential tube need to engage with the groove. Therefore, it is difficult to reduce the size of the lens barrel with increased space and layout efficiencies.
Even a lens barrel configured to be a three-stage-stretchable type for a high zoom magnification ratio requires a member that linearly moves and guides both the outer circumferential tube and the inner circumferential tube in the optical axis direction, increasing the size of the lens barrel in order to maintain a space for the member.